Did you ever find a way to open it?
Downloaded it again. Didn't work again. Sad emoji goes here.
Yeah I'm having the same problem :(
Everybody, you can solve it by this:
Assuming you downloaded the file and unzipped it to your Downloads folder:
chmod +x ~/Downloads/forma8_Mac/forma8.app/Contents/MacOS/forma8
Then right click it and Ctrl-Click “open” and in the warning, again click “open”.
Have fun.
Dennis
Another idea that could work is using the itch.io app. It's worked for me on other games so maybe it'll work her. Haven't tried myself yet.
Edit: yeah it works